1. Field of the Invention
This invention relates to an apparatus for reading images, such as characters formed on a sheet such as an original, while conveying the sheet, and in particular to a reading apparatus of the type which brings the sheet substantially into intimate contact with a reading portion.
Apparatuses of this type are often used, for example, in facsimile apparatuses or the like.
2. Related Background Art
An apparatus for reading the image of a sheet is disclosed, for example, in U.S. Pat. No. 4,438,918. In this apparatus, a sheet (an original) is fed along a predetermined conveyance path by a conveying roller. A slit is provided in the course of the conveyance path, and a light is applied to the original through the slit, and the reflected light is imaged on a photoelectric conversion element by a lens, whereby the image of the original is read. The photoelectric conversion element is disposed on a substrate in a direction perpendicular to the direction of conveyance of the original, receives the reflected light from the original, and converts it into an electrical signal.
In such an apparatus, however, the photoelectric conversion element can be disposed at a location within the apparatus into which it is difficult for outside light to enter, but a lens, a reflecting mirror, etc. are required, and this leads to bulkiness in the apparatus.
Also, an apparatus in which a lens array used to make the apparatus compact, and in which a photoelectric conversion element is disposed at a location near an original is disclosed in Japanese laid-Open Utility Model Application No. 57-188463. In an image reading apparatus using a lens array, the resolution is reduced unless the distance between the original and the lens array is kept constant. Therefore, in an image reading apparatus using a lens array in which an original is conveyed while being urged against a glass plate disposed at a predetermined distance from the lens array, the original is accurately positioned (see Japanese Laid-Open Utility Model Application No. 58-54169). The apparatus in which reading is effected with the original brought into contact with an image reading portion in this manner is called an "intimate contact type image reading apparatus".
In order to make such apparatus more compact, the assignee has developed a reading apparatus which does not use any lens but directly reads the image of an original using an image sensor. In this reading apparatus, a photoelectric conversion element is provided on a transparent plate disposed on a substrate having a hole therein for passing therethrough a light from a light source, and is covered with a protective transparent sheet. During the reading of the original, the photoelectric conversion element receives the reflected light of said light applied to the original being conveyed while being in contact with the protective transparent sheet, and converts it into an electrical signal.
In such an intimate contact type image reading apparatus, the original is conveyed while being urged against a reading portion by a roller in order that the original may be brought into intimate contact with the reading portion. Particularly, when the original is to be directly read by the photoelectric conversion element without the intermediary of a lens, if the original floats up even slightly from the protective transparent sheet, the resolving power will be reduced and the image will be blurred. To keep a high resolving power, use is made of a conveying roller for conveying the original while urging the original against the protective transparent sheet. Thus, when the original is not in the reading portion when the operation is started, the original conveying roller directly contacts the sensor. The reading portion of the sensor is constantly in frictional contact with the original and the conveying roller and therefore, the surface thereof is covered with a wear proof material. Also, it is indispensable for the surface of the reading portion to pass therethrough the reflected light from the original and therefore, a wear resisting layer chiefly composed of transparent glass is used as the surface of the recording portion.
The surface of this glass layer generally has a good property for intimate contact with the rubber surface of the conveying roller, and this means that the frictional force between the conveying roller and the glass layer is very great. Therefore, the motor for driving the conveying roller has been required to have a great output, and this has hampered the compactness and low cost of the apparatus.
Also, the use of a large motor of great torque would adversely affect other parts by the heat from the motor. There is a further problem of noise being produced when the glass and the conveying roller rub against each other.
Also, when a pulse motor is used as a drive source for the conveying roller and the original is fed in synchronism with the reading, there has been the possibility of unsatisfactory reading occurring due to deconditioning.
Furthermore, where the roller of the paper feeding portion and the conveying roller of the reading portion are driven by a common motor, there has been the problem that if the rotation of the conveying roller is stopped or becomes unstable due to the friction thereof with the glass, the rotation of the roller of the paper feeding portion also becomes unstable and paper feeding fails to take place.